An element of this type is known from U.S. Pat. No. 3,648,747, and also from the U.S. Pat. Nos. 5,340,251, 3,234,987 and 3,253,631.
Further elements of this type are known from the European patent application with the publication number EP-A-0 553 822 or the corresponding U.S. Pat. No. 5,340,251 and also from the European application with the publication number EP-A-0 669 473.
A similar element is also known from the European application with the publication number EP-A-0 663 247; however, this application is concerned with the manufacturing of an element of this kind rather than with the element itself.
Such elements are generally formed as elements with hollow bodies, or more precisely as nut elements, but could however also for example have a smooth cylindrical bore to receive a spigot. In addition, such elements could also be formed in the manner of bolt elements and in which case the head of the bolt element is secured to the sheet metal part or to the plate-like component and the head would have the above described design. Finally, the element can be regarded quite generally as a functional element, whereby it is possible to realize diverse functions. For example, the function of a nut through the provision of an element with a hollow body having an internal thread, or the function of a bolt by the provision of a shaft or spigot (tubular) part, or the function of for example a pin for the clamped attachment of other components, such as carpet eyes, or electrical terminals. Ultimately, it is not the function which is important, but rather the joint or attachment between the element and the plate-like component which normally consists of a sheet metal, but with other materials such as plastic panels is also possible.
The known elements in accordance with the above referenced patents and published applications are all elements having hollow bodies which are as a rule formed as nut elements. They all offer a certain degree of security against rotation (twist-out) so that on screwing-in a bolt element a rotation of the element having the hollow body is generally avoided. Moreover, the known elements have a certain press-out resistance. Nevertheless, improved security against rotation (twist-out) and higher press-out resistances are always desirable characteristics for such elements.
It has been shown with the known elements that the elements sometimes tear out of the plate-like component (normally a piece of sheet metal) in operation and under alternating loads. The manufacture of such elements having hollow bodies is also relatively complicated and a problem exists in as much as it is difficult to simultaneously keep the weight of the element small and to make the contact surface of sufficiently large dimensions.
The undercut in the side wall of the ring-shaped recess, which is necessary to produce the required press-out resistance of the hollow body is normally achieved by subjecting the element having a hollow body to a deformation or crushing process at the peripherally extending outer surface, whereby the side wall of the ring-shaped recess is brought from an initially axially parallel position into an inclined position. In this way, the opening to the ring-shaped recess between the pilot part and the now inclined side wall is reduced in comparison to the base surface of the recess and the undercut is produced. Through this crushing process, the element having the hollow body however also has an inclined flank at the outer jacket surface adjacent to the end face confronting the component. This can lead to a situation in which the contact surface at the end face of the element becomes too small, with the contact surface being so deformed during the attachment of the plate-like component that it acts in a knife-like cutting manner under load and a high surface pressure results between the component and the element having the hollow body.
As a result of this high surface pressure, the plate-like component yields or relaxes after a few hours of operation and the element is no longer as tightly attached to the component as desired. This leads eventually to settling or relaxation, so that the prestress of a bolt inserted into the element reduces to zero, whereby the bolted connection fails.
The inclined flank at the transition from the outer jacket surface into the end face of the element however also results in an unnecessary waste of material which is generally steel, because material which is present radially outside of the contact surface at the element does not provide any contribution to the strength of the connection or of the element. In other words, the elements are heavier than is absolutely necessary, which ultimately represents an economic disadvantage.